TFS: Volume Oscillator Strategy

This is the second part of TFS trading strategy. The concept of this
indicator is similar to that of On-Balance Volume indicator (OBV). It
is calculated according to these rules:
If Close > Open, Volume is positive
If Close < Open, Volume is negative
If Close = Open, Volume is neutral
Then you take the 7-day MA of the results.

WARNING:
- This script to change bars colors.